The present invention relates to a toothed belt, to a toothed belt power transmission apparatus, and to business equipment using such a toothed belt power transmission apparatus. The present invention belongs particularly to the technical field of reducing the nonuniformity of belt velocity, i.e., the variation in belt velocity.
Such a type of toothed belt has been known in the art. In the past, toothed belts having belt teeth of trapezoidal profile were used. However, for the achievement of higher power transmission and for the further reduction in noise, belts with a tooth profile having flank surfaces of convex profile have been proposed. Such a type of belt has now been used extensively nowadays. One of such tooth profiles is shown in Japanese Unexamined Patent Application Gazette No. S50-42252, which is known in the art as the STPD tooth profile. The other tooth profile is shown in Japanese Unexamined Patent Application Gazette No. S59-89852, which is known in the art as the HTD-II tooth profile. The former tooth profile, i.e., the STPD tooth profile, has been put to practical use (for example, SUPER TORQUE SYNCRO BELT, a product of BANDO CHEMICAL INDUSTRIES, LTD.). The latter tooth profile, i.e., the HTD-II tooth profile, has been also put to practical use (for example, POWER GRIP GT BELT, a product of UNITTA COMPANY). Further, Japanese Unexamined Patent Application Gazette No. S64-74341 shows and proposes a toothed belt for the purpose of accurate location drive of movable parts incorporated in a business machine. More specifically, as shown in FIG. 17, a plurality of belt tooth portions 11xe2x80x2, 11xe2x80x3, . . . (only one of which is shown in the figure) are provided along a land line LL of a main body 9xe2x80x2 of a belt 8xe2x80x2 at their fixed pitch. Each belt tooth portion 11xe2x80x2 comprises tooth root portions 12xe2x80x2 formed of circularly arcuate surfaces which are arranged symmetrically with each other in respect to a centerline C2 in the tooth width direction, power transmission portions 13xe2x80x2, 13xe2x80x2 formed of circularly arcuate surfaces of convex profile which contiguously adjoin the tooth root portions 12xe2x80x2, 12xe2x80x2 and are arranged symmetrically with each other in respect to the tooth width direction centerline C2, and tooth tip portions 14xe2x80x2, 14xe2x80x2 formed of circularly arcuate surfaces which contiguously adjoin the power transmission portions 13xe2x80x2, 13xe2x80x2 and are arranged symmetrically with each other in respect to the tooth width direction centerline C2, wherein these tooth tip portions 14xe2x80x2, 14xe2x80x2 are interconnected by a tooth crest surface 15xe2x80x2 formed of a flat surface. When the toothed belt 8xe2x80x2 is in static meshing engagement with a toothed pulley 1xe2x80x2, the tooth root portion 12xe2x80x2 of each of the belt tooth portions 11xe2x80x2 substantially comes into contact with a tooth top arc portion 4xe2x80x2 of a pulley tooth groove portion 3xe2x80x2. The backlash of the belt tooth portion 11xe2x80x2 at the pulley tooth groove portion 3xe2x80x2 gradually increases from the tooth root portion to the tooth tip portion of the belt tooth portion 11xe2x80x2 and the depth of the pulley tooth groove portion 3xe2x80x2 exceeds the height of the belt tooth portion 11xe2x80x2. In this prior art example, the backlash with the pulley tooth groove portion 3xe2x80x2 is reduced to zero at the tooth root portion 12xe2x80x2 of the belt tooth portion 11xe2x80x2, while the backlash with the pulley tooth groove portion 3xe2x80x2 is gradually increased from the tooth root portion to the tooth tip portion of the belt tooth portion 11xe2x80x2 so that the belt tooth portion 11xe2x80x2 tapers toward the tooth tip portion, thereby to suppress meshing interference between the belt tooth portion 11xe2x80x2 and the tooth top arc portion 4xe2x80x2 of the pulley tooth groove portion 3xe2x80x2 for the reduction of belt pitch line variation due to such meshing interference. In FIG. 17, tooth groove flank surface portions of concave profile of the pulley tooth groove portion 3xe2x80x2 are assigned the reference numeral 5xe2x80x2, a tooth groove bottom portion is assigned the reference numeral 6xe2x80x2, and the pitch line of the belt 8xe2x80x2 is denoted by PL, which corresponds to the pitch circle of the pulley 1xe2x80x2. Further, for the purpose of providing an easy understanding, in FIG. 17 the outer peripheral portion of the pulley 1xe2x80x2 is shown in expanded fashion, together with the belt 8xe2x80x2.
Apart from the above, in a typical business machine such as a printer and photocopier, a character printing (including printing of images) device making utilization of a toothed belt power transmission apparatus is used widely. In such a printer, a carriage carrying thereon an ink supply and a printing mechanism such as a hammer is attached to a toothed belt. The toothed belt is wound around toothed pulleys and the pulleys are forwarded and reversed to cause the carriage to reciprocate.
In order to enable the carriage to provide improved printing accuracy and image quality, it is required that the nonuniformity of velocity of the toothed belt when traveling over the pulleys (i.e., the belt velocity variation) be reduced as low as possible. Particularly, for the case of printers, there have been made rapid improvements in color printing, color printing speed-up, color printing quality. The meshing vibration (velocity nonuniformity caused by meshing) of toothed belt may cause printing nonuniformity and image nonuniformity, so that there have been strong demands for the reduction of the nonuniformity of belt velocity caused by meshing.
For the case of equipment for business use such as a printer, a toothed belt, such as an STPD toothed belt or HTD-II toothed belt, is commonly used, wherein the tooth pitch is set below 3 mm (for example, either 3 mm, 2 mm, or 1.5 mm), and the tooth has a profile which is just a scaledown of the tooth profile of relatively large tooth pitch such as 8-mm pitch or 5-mm pitch.
However, these tooth profiles were originally developed for use in high power transmission, in which no scheme to meet demands for the reduction of the nonuniformity of velocity was taken into consideration at all. Although the toothed belt of the foregoing prior art (S64-74341) was proposed taking into account the occurrence of belt velocity nonuniformity to some extent, it failed to provide a tooth profile optimum for the reduction of the nonuniformity of velocity. This prior art technique is therefore unable to reduce the nonuniformity of belt velocity to a sufficient extent.
In fact, little research in tooth profile has been done for the reduction of toothed belt velocity nonuniformity. Bearing in mind the above, the present invention was made by the inventor who intensively conducted analysis and experiments on various factors constituting a tooth profile of a toothed belt for use in equipment for business use or the like. Accordingly, an object of the present invention is to reduce the nonuniformity of toothed belt velocity as low as possible.
In order to achieve the above-described object, the inventor conducted research. The research result had shown that, for the case of toothed belts having tooth portions with convex flank surface portions, the flank maximum pressure angle had considerable influence on the nonuniformity of velocity. This factor had not at all been taken into consideration before. That is to say, in conventional toothed belts having either an STPD tooth profile or an HTD-II tooth profile for use in high power transmission applications, the maximum pressure angle of the tooth flank surface is set low for the avoidance of tooth jumping occurring during high power transmission operation. For example, for an STPD tooth profile whose tooth pitch is between 1.5 mm and 3.0 mm, the flank maximum pressure angle is set to fall in the range between an angle of 14.2 degrees and an angle of 14.4 degrees, while, for an HTD-II tooth profile whose tooth pitch between 1.5 mm and 3.0 mm, the flank maximum pressure angle is set to fall in the range between an angle of 7.5 degrees and an angle of 8.1 degrees. On the other hand, for the case of toothed belts that find applications in equipment for business use, they are driven under low power transmission conditions. Therefore, there is almost no need to take into account belt tooth jumping. The research result by the inventor shows that the nonuniformity of belt velocity can be reduced to a considerable extent if the flank maximum pressure angle is set to fall in the range between an angle of 15 degrees and an angle of 25 degrees.
As an embodiment of the above finding, the present invention provides a toothed belt which comprises a belt main body with a pitch line on which a tensile member is embedded therein and a plurality of belt tooth portions provided at a fixed pitch on a land line of the belt main body. Each of the belt tooth portions comprises tooth root portions formed of circularly arcuate surfaces which are arranged symmetrically with each other in respect to a centerline in the tooth width direction, power transmission portions formed of circularly arcuate surfaces of convex profile which contiguously adjoin the tooth root portions, lie at flank surfaces of the tooth portion, and are arranged symmetrically with each other in respect to the tooth width direction centerline, tooth tip portions formed of circularly arcuate surfaces which contiguously adjoin the power transmission portions and are arranged symmetrically with each other in respect to the tooth width direction centerline, and a tooth crest surface formed of an approximately flat surface which interconnects the tooth tip portions, wherein the maximum pressure angle at where the power transmission portion of the belt tooth flank surface and the tooth root portion are connected together is between an angle of 15 degrees and an angle of 25 degrees.
At the time when a tooth portion of the toothed belt comes into meshing engagement with a driving-side tooth groove portion of the toothed pulley, such engagement of the belt tooth portion with the pulley tooth groove portion takes place at a location which is somewhat delayed with respect to the location of the pulley tooth groove portion because of the influence of load torque that is applied. Consequently, an aft flank surface of the belt tooth portion in respect to the traveling direction is first brought into contact with a flank surface of the pulley tooth groove portion. Thereafter, the belt tooth portion slides into the pulley tooth groove portion. At this time, at a span of the belt (i.e., at a belt portion that is not being wound around the pulley), the belt pitch line moves vertically in a direction normal to the belt span, resulting in the occurrence of meshing velocity nonuniformity. The amount of vertical movement of the belt pitch line is determined by a reaction force produced when the belt tooth portion slides into the pulley tooth groove portion and a component of a belt tension force produced when the belt is pushed upward by the reaction force. Because of this, as the contact position moves away from the perfect meshing position of the belt tooth portion and the pulley tooth groove portion, the belt tension force component decreases, thereby increasing the amount of upward movement of the belt pitch line. In other words, earlier contacting of the belt tooth portion with the pulley tooth groove portion results in greater velocity nonuniformity. Therefore, if the maximum pressure angle is small as in the conventional tooth profiles, then the contacting of the belt tooth flank surface with the pulley tooth groove flank surface takes place early (see FIG. 4(b)). On the other hand, if the maximum pressure angle is set larger in comparison with the conventional techniques, this delays the contacting of the belt tooth flank surface with the pulley tooth groove flank surface (see FIG. 4(a)), thereby reducing the nonuniformity of belt velocity.
However, the maximum pressure angle cannot be increased excessively and if the maximum pressure angle is too great, this will not reduce the nonuniformity of velocity; rather the nonuniformity of velocity increases. That is to say, as described above, the amount of shift of the belt span is determined by reaction force (produced when the belt tooth portion slides into the pulley tooth groove portion after their flank surfaces come into contact with each other) and belt tension force component. However, at that time, if the maximum pressure angle is too great, then a component of a reaction force in the vertical direction (i.e., in the direction normal to the belt span) produced when the belt tooth portion slides into the pulley tooth groove portion becomes too great. This will not allow the belt tooth portion to smoothly slide into the pulley tooth groove portion, therefore pushing up the belt pitch line to increase the nonuniformity of velocity.
The analysis result obtained by the inventor shows that an optimal allowable range for the maximum pressure angle is between an angle of 15 degrees and an angle of 25 degrees as described above. In comparison with the commonly-used pressure angle range (between an angle of 14.2 degrees and an angle of 14.4), the present invention is able to reduce the nonuniformity of velocity more effectively.
Further, the maximum pressure angle at where the power transmission portion of the belt tooth flank surface and the tooth root portion are connected together is between an angle of 16 degrees and an angle of 23 degrees. Furthermore, the maximum pressure angle is between an angle of 17 degrees and an angle of 22 degrees. As a result of such arrangement, the nonuniformity of velocity can be reduced to a further extent.
The present invention provides a toothed belt comprising a belt main body with a pitch line on which a tensile member is embedded therein and a plurality of belt tooth portions provided at a fixed pitch on a land line of the belt main body. Each of the belt tooth portions comprises tooth root portions formed of circularly arcuate surfaces which are arranged symmetrically with each other in respect to a centerline in the tooth width direction, power transmission portions formed of circularly arcuate surfaces of convex profile which contiguously adjoin the tooth root portions, lie at flank surfaces of the tooth portion, and are arranged symmetrically with each other in respect to the tooth width direction centerline, and a tooth tip end portion formed of a circularly arcuate surface which is so provided as to interconnect the power transmission portions and whose center point lies on the tooth width direction centerline, wherein the maximum pressure angle at where the power transmission portion of the belt tooth flank surface and the tooth root portion are connected together is between an angle of 15 degrees and an angle of 25 degrees.
Such a tooth construction is able to provide the same effects as above. Further, since the tooth tip end portion of the belt tooth portion is defined by a single circularly arcuate surface, this makes it possible to further delay the contacting of the belt tooth portion with the pulley tooth groove portion in comparison with increasing only the maximum pressure angle (see the virtual line of FIG. 8). Accordingly, the nonuniformity of belt velocity can be reduced to a further extent.
In such a case, the maximum pressure angle in the toothed belt is between an angle of 16 degrees and an angle of 23 degrees. Further, the maximum pressure angle is between an angle of 17 degrees and an angle of 22 degrees. As a result of such setting, the nonuniformity of velocity of the toothed belt can be reduced to a further extent.
The present invention provides a toothed belt power transmission apparatus comprising a combination of any one of the preceding toothed belts and toothed pulleys each having a plurality of pulley tooth groove portions which are provided at a fixed pitch on a pulley outside diameter line. Each of the pulley tooth groove portions comprises tooth top arc portions formed of circularly arcuate surfaces which are arranged symmetrically with each other in respect to a centerline in the tooth groove width direction, tooth groove flank surface portions formed of circularly arcuate surfaces of concave profile which contiguously adjoin the tooth top arc portions and are arranged symmetrically with each other in respect to the tooth groove width direction centerline, and a tooth groove bottom portion provided so as to interconnect the tooth groove flank surface portions. The belt tooth portion has flank surfaces whose profile is substantially the same as that of flank surfaces of the pulley tooth groove portion. Further, in a power transmission state (i.e., in a working state) in which the toothed belt is wound around the toothed pulleys and a tension force is applied to the toothed belt, the pressure angles of the belt tooth portion flank surface and the pulley tooth groove portion flank surface at their respective locations in the tooth height direction are made approximately equal to each other and a belt land portion comes into contact with a pulley outside diameter portion.
As described above, if the maximum pressure angle is so increased as to fall within the range below 25 degrees (preferably, between an angle of 17 degrees and an angle of 22 degrees), this delays the belt tooth flank surface to come into contact with the pulley tooth groove flank surface, resulting in reducing the nonuniformity of belt velocity. Other than this, even when the pressure angle of the belt tooth portion remains small as in the conventional techniques, it is possible to geometrically delay, within the delay range of the pulley tooth groove portion with respect to the belt tooth portion during low power torque transmission, the contacting of the belt tooth flank surface with the pulley tooth groove flank surface by setting the maximum pressure angle of the pulley tooth groove portion smaller than that of the belt tooth portion. As described above, if the maximum pressure angle of the pulley tooth groove portion is made smaller than that of the belt tooth portion, then the backlash between the belt tooth portion and the pulley tooth groove portion~gradually increases from root to tip. This is the same construction as shown in the prior art technique (JP Unexamined Patent Application Gazette No. S64-74341).
However, the inventor""s research shows that if the maximum pressure angle of the pulley tooth groove portion is set smaller than the maximum pressure angle of the belt tooth portion, this increases the nonuniformity of velocity of the belt. That is to say, when the maximum pressure angle of the pulley tooth groove portion is set smaller than the maximum pressure angle of the belt tooth portion, this certainly delays the contacting of the belt tooth flank surface with the pulley tooth groove flank surface; however, the belt tooth flank surface is brought into contact, not with the pulley tooth groove flank surface but with the tooth top arc portion (see FIG. 5(b)). As a consequence of such contact, the belt tooth portion is pushed up by the tooth top arc portion of the pulley tooth groove-portion, so that the belt tooth portion is unable to smoothly slide into the pulley tooth groove portion and the belt pitch line is pushed up, resulting in increasing the nonuniformity of velocity.
On the other hand, according to the toothed belt power transmission apparatus of the present invention, it is arranged such that the pressure angles of the belt tooth portion flank surface and the pulley tooth groove portion flank surface at their respective locations in the tooth height direction are made approximately equal to each other, so that the belt tooth flank surface comes into uniform contact with the pulley tooth groove flank surface. This allows the belt tooth portion to smoothly slide into the pulley tooth groove portion (see FIG. 5(a)). The belt pitch line will not be pushed up, which considerably reduces the nonuniformity of velocity of the belt.
Further, an arrangement may be made, in which the pulley tooth groove portion of the toothed pulley has a tooth groove bottom portion which is formed of an approximately flat surface. As a result of such arrangement, the tooth groove bottom portion of the pulley tooth groove portion and the tooth crest surface of the belt tooth portion are formed of identical, approximately flat surfaces, which is preferable. The tooth groove bottom portion may be formed of a surface inscribing an arc of a circle having its center in the pulley central direction.
The present invention provides a toothed belt power transmission apparatus comprising a combination of the foregoing toothed belt and toothed pulleys each having a plurality of pulley tooth groove portions which are provided at a fixed pitch on a pulley outside diameter line. Each of the pulley tooth groove portions comprises tooth top arc portions formed of circularly arcuate surfaces which are arranged symmetrically with each other in respect to a centerline in the tooth groove width direction, tooth groove flank surface portions formed of circularly arcuate surfaces of concave profile which contiguously adjoin the tooth top arc portions and are arranged symmetrically with each other in respect to the tooth groove width direction centerline, and a tooth groove bottom portion provided so as to interconnect the tooth groove flank surface portions, wherein the belt tooth portion has flank surfaces whose profile is substantially the same as that of flank surfaces of the pulley tooth groove portion and wherein in a power transmission state in which the toothed belt is wound around the toothed pulleys and a tension force is applied to the toothed belt, the pressure angles of the belt tooth portion flank surface and the pulley tooth groove portion flank surface at their respective locations in the tooth height direction are made approximately equal to each other and a belt land portion comes into contact with a pulley outside diameter portion. This construction is also able to provide the same operation and effects as the above.
Furthermore, in the foregoing toothed belt power transmission apparatus of the present invention, the pulley tooth groove portion of each of the toothed pulleys has a tooth groove bottom portion which comprises a circularly arcuate surface inscribing an arc of a circle whose center point lies on the tooth groove width direction centerline and whose radius is greater than that of the tooth tip end portion of the belt tooth portion. That is to say, in the case the belt tooth portion has a tooth tip end portion which is a circularly arcuate surface (i.e., a curvilinear surface inscribing the arc of a circle), the pulley tooth groove portion may have a tooth groove bottom portion which is an approximately flat surface. In the present invention, however, the tooth groove bottom portion of the pulley tooth groove portion is formed of a circularly arcuate surface whose radius is greater than that of the tooth tip end portion of the belt tooth portion. This arrangement is preferable because the belt tooth portion is able to slide into the pulley tooth groove portion in a much smoother manner.
The present invention provides a toothed belt power transmission apparatus comprising a combination of a toothed belt and toothed pulleys. The toothed belt has a belt main body with a pitch line on which a tensile member is embedded therein, a plurality of belt tooth portions provided at a fixed pitch in the belt main body, and a land portion provided between adjacent belt tooth portions. Each of the belt tooth portions has power transmission portions formed of circularly arcuate surfaces of convex profile which lie at flank surfaces of the tooth portion and are arranged symmetrically with each other in respect to a centerline in the tooth width direction, tooth tip portions formed of circularly arcuate surfaces which contiguously adjoin the power transmission portions and are arranged symmetrically with each other in respect to the tooth width direction centerline, and a tooth crest surface formed of an approximately flat surface which is so provided as to interconnect the tooth tip portions. On the other hand, each of the toothed pulleys has a plurality of pulley tooth groove portions provided at a fixed pitch on a pulley outside diameter line. Each of the pulley tooth groove portions has tooth top arc portions formed of circularly arcuate surfaces which are arranged symmetrically with each other in respect to a centerline in the tooth groove width direction, tooth groove flank surface portions formed of circularly arcuate surfaces of concave profile which contiguously adjoin the tooth top arc portions and are arranged symmetrically with each other in respect to the tooth groove width direction centerline, and a tooth groove bottom portion provided so as to interconnect the tooth groove flank surface portions. The maximum pressure angle at where the tooth top arc portion and the tooth groove flank surface portion in the pulley tooth groove portion are connected together is between an angle of 15 degrees and an angle of 25 degrees and the belt tooth portion has flank surfaces whose profile is substantially the same as that of flank surfaces of the pulley tooth groove portion. Moreover, in a power transmission state in which the toothed belt is wound around the toothed pulleys and a tension force is applied to the toothed belt, the pressure angles of the belt tooth portion flank surface and the pulley tooth groove portion flank surface at their respective locations in the tooth height direction are made approximately equal to each other and a belt land portion does not come into contact with a pulley outside diameter portion.
The arrangement for reducing the nonuniformity of belt velocity by increasing the maximum pressure angle is effective for toothed belt power transmission apparatus that are used in such a condition that the belt land portion does not come into contact with a pulley outside diameter portion. However, in such a case, areas of the belt land portion, the tooth root portion of the tooth portion, and the tooth flank surface that lie outside beyond the pulley outside diameter portion in the radial direction have no direct influence on the behaviors of the belt tooth portion at the time of meshing. Accordingly, the maximum pressure angle of the belt tooth portion in the belt alone is not important, but the maximum pressure angle at a connection point of the tooth top arc portion and the tooth groove flank surface portion is important. In accordance with the present invention, the maximum pressure angle at where the tooth top arc portion and the tooth groove flank surface portion are connected together is between an angle of 15 degrees and an angle of 25 degrees, as a result of which arrangement the same operation and effects as the above can be obtained.
In the above-described toothed belt power transmission apparatus, the land portion of the toothed belt comprises an approximately flat surfaces which is interconnected with the belt tooth portion flank surfaces through tooth root portions formed of circularly arcuate surfaces which are arranged symmetrically with the tooth width direction centerline.
The land portion of the belt, since there is no constraint when taking into account the nonuniformity of belt velocity, may be formed of a circularly arcuate surface; however, it is preferable that the belt land portion be formed of an approximately flat surface. That is to say, toothed belts made of polyurethane have been used widely in equipment for business use because they are superior in the shape accuracy of tooth portions or the like. Particularly, when the belt tooth portion pitch is below 1.5 mm, nearly all of toothed belts are made of polyurethane, for rubber belts are not able to meet requirements of the business equipment because they are poor in tooth shape accuracy. In such a polyurethane toothed belt, a concave portion is practically provided in the belt land portion in order to separate the core cord from the land line. However, when the belt tooth portion pitch is below 1.5 mm, the formation dimensions of such a concave portion are considerably small, resulting in difficult die processing. In order to cope with such a problem, the core cord is provided directly over the land line without the provision of the foregoing concave portion, and the belt is used in such a condition that the belt land portion is not brought into contact with a pulley outside diameter portion so as to prevent the core cord from being damaged by contact with the pulley outside diameter portion. In such a case, since in the present invention the belt land portion is an approximately flat surface, the position of the core cord can be made stable by the belt land portion which is approximately flat.
In such a case, the maximum pressure angle at where the tooth top arc portion and the tooth groove flank surface portion in the pulley tooth groove portion of the toothed belt power transmission apparatus are connected together is between an angle of 16 degrees and an angle of 23 degrees. Further, the maximum pressure angle is between an angle of 17 degrees and an angle of 22 degrees. As a result of such arrangement, the nonuniformity of toothed belt velocity can be reduced to a further extent.
Further, in the present invention, the pulley tooth groove portion of the toothed pulley has a tooth groove bottom portion which is formed of an approximately flat surface. As a result of such arrangement, when the belt is wound around the pulley, the toot tip end portion of the belt tooth portion can be received at the tooth groove bottom portion of the pulley tooth groove portion whose area is large. This makes it possible to stabilize the core cord position (pitch line) of the belt when wound around the pulley. This reduces the nonuniformity of velocity to a further extent.
The present invention provides a toothed belt power transmission apparatus comprising a combination of a toothed belt and toothed pulleys. The toothed belt has a belt main body with a pitch line on which a tensile member is embedded therein, a plurality of belt tooth portions provided at a fixed pitch in the belt main body, and a land portion provided between adjacent belt tooth portions. Each of the belt tooth portions has power transmission portions formed of circularly arcuate surfaces of convex profile which lie at flank surfaces of the tooth portion and are arranged symmetrically with each other in respect to a centerline in the tooth width direction and a tooth tip end portion formed of a circularly arcuate surface which is so provided as to interconnect the power transmission portions and whose center point lies on the tooth width direction centerline. On the other hand, each of the toothed pulleys has a plurality of pulley tooth groove portions provided at a fixed pitch on a pulley outside diameter line. Each of the pulley tooth groove portions has tooth top arc portions formed of circularly arcuate surfaces which are arranged symmetrically with each other in respect to a centerline in the tooth groove width direction, tooth groove flank surface portions formed of circularly arcuate surfaces of concave profile which contiguously adjoin the tooth top arc portions and are arranged symmetrically with each other in respect to the tooth groove width direction centerline, and a tooth groove bottom portion provided so as to interconnect the tooth groove flank surface portions. The maximum pressure angle at where the tooth top arc portion and the tooth groove flank surface portion in the pulley tooth groove portion are connected together is between an angle of 15 degrees and an angle of 25 degrees. The belt tooth portion has flank surfaces whose profile is substantially the same as that of flank surfaces of the pulley tooth groove portion. In a power transmission state in which the toothed belt is wound around the toothed pulleys and a tension force is applied to the toothed belt, the pressure angles of the belt tooth portion flank surface and the pulley tooth groove portion flank surface at their respective locations in the tooth height direction are made approximately equal to each other and a belt land portion does not come into contact with a pulley outside diameter portion.
That is to say, in accordance with the toothed belt power transmission apparatus of the present invention, the construction of the belt tooth portion is changed to the same one as the above and the same operation and effects as the above can be obtained.
In such a case, the land portion of the toothed belt in the toothed belt power transmission apparatus comprises an approximately flat surface which is interconnected with the belt tooth portion flank surfaces through tooth root portions formed of circularly arcuate surfaces which are arranged symmetrically with the tooth width direction centerline. Such arrangement provides the same effects as the above.
Further, in accordance with the toothed belt power transmission apparatus of the present invention, the maximum pressure angle at where the tooth top arc portion and the tooth groove flank surface portion in the pulley tooth groove portion are connected together is between an angle of 16 degrees and an angle of 23 degrees. Moreover, the maximum pressure angle is between an angle of 17 degrees and an angle of 22 degrees. As a result of such arrangement, the nonuniformity of toothed belt velocity can be reduced to a further extent.
In accordance with the toothed belt power transmission apparatus, the pulley tooth groove portion of the toothed pulley has a tooth groove bottom portion which comprises a circularly arcuate surface inscribing an arc of a circle whose center point lies on the tooth groove width direction centerline and whose radius is greater than that of the tooth tip end portion of the belt tooth portion. Such arrangement provides the same effects as the above.
Finally, the present invention provides equipment for use in business applications which is provided with a toothed belt power transmission apparatus formed in accordance with the present invention wherein a carriage is attached to the toothed belt. As a result of such arrangement, during the operating time of the toothed belt power transmission apparatus, when the carriage is shifted for performing character printing, the variation in carriage velocity caused by the nonuniformity of belt velocity is reduced. This makes it possible for the carriage to provide improved printing accuracy and image quality.